Pyridoneindoaniline dye-donor element for thermal dye transfer
This invention relates to pyridoneindoaniline dye-donor elements used in thermal dye transfer which have good hue, dye stability and high transfer densities. 
     In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled &#34;Apparatus and Method For Controlling A Thermal Printer Apparatus,&#34; issued Nov. 4, 1986, the disclosure of which is hereby incorporated by reference. 
     A problem has existed with the use of certain dyes in dye-donor elements for thermal dye transfer printing. Many of the dyes proposed for use do not have adequate stability to light. Others do not have good hue or yield high transfer densities. It would be desirable to provide dyes which have good light stability, have improved hues and give high transfer densities. 
     In EP 035,235, DE 2,808,825, GB 2,070,795 and BE 872,201, there is a disclosure of pyridoneindoaniline dyes for use in silver halide-based dye-bleach systems. In JP 63/247,092, there is a disclosure of pyridoneindoaniline dyes for use in optical recording materials. There is no teaching in these references, however, that these dyes could be used in thermal dye transfer systems. 
     It would be desirable to provide pyridoneindoaniline dyes for thermal dye transfer imaging which give high transfer densities, have improved hues and good stability to heat and light. 
     Substantial improvements in light stability, transfer density and hues are achieved in accordance with this invention which comprises a dye-donor element for thermal dye transfer comprising a support having thereon a dye dispersed in a polymeric binder, the dye comprising a pyridoneindoaniline dye having the formula: ##STR2## wherein: R 1  and R 2  each independently represents hydrogen; an alkyl group having from 1 to about 6 carbon atoms; a cycloalkyl group having from about 5 to about 7 carbon atoms; allyl; an aryl group having from about 6 to about 10 carbon atoms; or hetaryl; or such alkyl, cycloalkyl, allyl, aryl or hetaryl groups substituted with one or more groups such as alkyl, aryl, alkoxy, aryloxy, amino, halogen, nitro, cyano, thiocyano, hydroxy, acyloxy, acyl, alkoxycarbonyl, aminocarbonyl, alkoxycarbonyloxy, carbamoyloxy, acylamido, ureido, imido, alkylsulfonyl, arylsulfonyl, alkylsulfonamido, arylsulfonamido, alkylthio, arylthio, trifluoromethyl, etc., e.g., methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, methoxyethyl, benzyl, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, cyclohexyl, cyclopentyl, phenyl, pyridyl, naphthyl, thienyl, pyrazolyl, p-tolyl, p-chlorophenyl, m-(N-methyl-sulfamoyl)phenylmethyl, methylthio, butylthio, benzylthio, methanesulfonyl, pentanesulfonyl, methoxy, ethoxy, 2-methane-sulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonyl-methyl, imidazolyl, naphthyloxy, furyl, p-tolylsulfonyl, p-chlorophenylthio, m-(N-methyl sulfamoyl)phenoxy, ethoxycarbonyl, methoxyethoxycarbonyl, aryloxycarbonyl, acetyl, benzoyl, N,N-dimethylcarbamoyl, dimethylamino, morpholino, anilino, pyrrolidino, etc.; or 
     R 1  and R 2  can be joined together to form, along with the nitrogen to which they are attached, a 5- to 7-membered heterocyclic ring such as morpholine or pyrrolidine; or 
     either or both of R 1  and R 2  can be combined with R 3  to form a 5- to 7-membered heterocyclic ring; 
     each R 3  independently represents substituted or unsubstituted alkyl, cycloalkyl, allyl, aryl or hetaryl as described above for R 1  and R 2  ; alkoxy, aryloxy, halogen, nitro, cyano, thiocyano, hydroxy, acyloxy, acyl, alkoxycarbonyl, aminocarbonyl, alkoxycarbonyloxy, carbamoyloxy, acylamido, ureido, imido, alkylsulfonyl, arylsulfonyl, alkylsulfonamido, arylsulfonamido, alkylthio, arylthio or trifluoromethyl; or 
     any two of R 3  may be combined together to form a 5- or 6-membered carbocyclic or heterocyclic ring; or 
     one or two of R 3  may be combined with either or both of R 1  and R 2  to complete a 5- to 7-membered ring; 
     m is an integer of from 0 to 4; 
     R 4  and R 5  each independently represents hydrogen; a substituted or unsubstituted alkyl, aryl or hetaryl group as described above for R 1  and R 2  ; or an electron withdrawing group such as cyano, alkoxycarbonyl, aminocarbonyl, alkylsulfonyl, arylsulfonyl, acyl, nitro, etc.; 
     R 6  represents hydrogen; a substituted or unsubstituted alkyl, aryl or hetaryl group as described above for R 1  and R 2  ; NH 2 , NHR 1 , NR 1  R 2 , NHCOR 1 , NHSO 2  R 1  or OR 1 . 
     In a preferred embodiment of the invention, R 1  and R 2  are each ethyl. In another preferred embodiment, R 3  is hydrogen or methyl. In yet another preferred embodiment, R 4  is methyl or phenyl. In still another preferred embodiment, R 5  is cyano. In yet another preferred embodiment, R 6  is n--C 4  H 9 , NHCOC 4  H 9  --t, NH 2 , c--C 6  H 11  or phenyl. 
     Compounds included within the scope of the invention include the following: 
     
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 ##STR3##                                                                 
Compound     R.sup.3  R.sup.4   R.sup.6                                   
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1            H        C.sub.6 H.sub.5                                     
                                n-C.sub.4 H.sub.9                         
2            H        C.sub.6 H.sub.5                                     
                                NHCOC.sub.4 H.sub.9 -t                    
3            H        CH.sub.3  n-C.sub.4 H.sub.9                         
4            CH.sub.3 CH.sub.3  n-C.sub.4 H.sub.9                         
5            H        CH.sub.3  NHCOC.sub.4 H.sub.9 -t                    
6            CH.sub.3 CH.sub.3  NHCOC.sub.4 H.sub.9 -t                    
7            H        C.sub.6 H.sub.5                                     
                                NH.sub.2                                  
8            CH.sub.3 C.sub.6 H.sub.5                                     
                                NH.sub.2                                  
9            H        CH.sub.3  c-C.sub.6 H.sub.11                        
10           H        CH.sub.3  C.sub.6 H.sub.5                           
11           CH.sub.3 C.sub.6 H.sub.5                                     
                                NHCOC.sub.4 H.sub.9 -t                    
12           CH.sub.3 CH.sub.3  c-C.sub.6 H.sub.11                        
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13                                                                        
      ##STR4##                                                            
14                                                                        
      ##STR5##                                                            
15                                                                        
      ##STR6##                                                            
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     The above dyes may be prepared analogously to the methods described in DE 2,808,825 and JP 63/247,092 described above. 
     A dye-barrier layer may be employed in the dye-donor elements of the invention to improve the density of the transferred dye. Such dye-barrier layer materials include hydrophilic materials such as those described and claimed in U.S. Pat. No. 4,716,144 by Vanier, Lum and Bowman. 
     The dye in the dye-donor of the invention is dispersed in a polymeric binder such as a cellulose derivative, e.g., cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate or any of the materials described in U.S. Pat. No. 4,700,207; a polycarbonate; polyvinyl acetate; poly(styrene-co-acrylonitrile); a poly(sulfone) or a poly(phenylene oxide). The binder may be used at a coverage of from about 0.1 to about 5 g/m 2 . 
     The dye layer of the dye-donor element may be coated on the support or printed thereon by a printing technique such as a gravure process. 
     Any material can be used as the support for the dye-donor element of the invention provided it is dimensionally stable and can withstand the heat of the laser or thermal head. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; cellulose esters such as cellulose acetate; fluorine polymers such as polyvinylidene fluoride or poly(teterfluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, polypropylene or methylpentene polymers; and polyimides such as polyimide-amides and polyether-imides. The support generally has a thickness of from about 5 to about 200 μm. It may also be coated with a subbing layer, if desired, such as those materials described in U.S. Pat. Nos. 4,695,288 or 4,737,486. 
     The reverse side of the dye-donor element may be coated with a slipping layer to prevent the printing head from sticking to the dye-donor element. Such a slipping layer would comprise either a solid or liquid lubricating material or mixtures thereof, with or without a polymeric binder or a surface active agent. Preferred lubricating materials include oils or semi-crystalline organic solids that melt below 100° C. such as poly(vinyl stearate), beeswax, perfluorinated alkyl ester polyethers, poly(caprolactone), silicone oil, poly(tetrafluoroethylene), carbowax, poly(ethylene glycols), or any of those materials disclosed in U.S. Pat. Nos. 4,717,711; 4,717,712; 4,737,485; and 4,738,950. Suitable polymeric binders for the slipping layer include poly(vinyl alcohol-co-butyral), poly(vinyl alcohol-co-acetal), poly(styrene), poly(vinyl acetate), cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate or ethyl cellulose. 
     The amount of the lubricating material to be used in the slipping layer depends largely on the type of lubricating material, but is generally in the range of about 0.001 to about 2 g/m 2 . If a polymeric binder is employed, the lubricating material is present in the range of 0.1 to 50 weight %, preferably 0.5 to 40, of the polymeric binder employed. 
     The dye-receiving element that is used with the dye-donor element of the invention usually comprises a support having thereon a dye image-receiving layer. The support may be a transparent film such as a poly(ether sulfone), a polyimide, a cellulose ester such as cellulose acetate, a poly(vinyl alcohol-co-acetal) or a poly(ethylene terephthalate). The support for the dye-receiving element may also be reflective such as baryta-coated paper, polyethylene-coated paper, an ivory paper, a condenser paper or a synthetic paper such as duPont Tyvek®. Pigmented supports such as white polyester (transparent polyester with white pigment incorporated therein) may also be used. 
     The dye image-receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, poly(styrene-co-acrylonitrile), poly(caprolactone), a poly(vinyl acetal) such as poly(vinyl alcohol-co-butyral), poly(vinyl alcohol-co-benzal), poly(vinyl alcohol-co-acetal) or mixtures thereof. The dye image-receiving layer may be present in any amount which is effective for the intended purpose. In general, good results have been obtained at a concentration of from about 1 to about 5 g/m 2 . 
     As noted above, the dye-donor elements of the invention are used to form a dye transfer image. Such a process comprises imagewise-heating a dye-donor element as described above and transferring a dye image to a dye-receiving element to form the dye transfer image. 
     The dye-donor element of the invention may be used in sheet form or in a continuous roll or ribbon. If a continuous roll or ribbon is employed, it may have only the dye thereon as described above or may have alternating areas of other different dyes, such as sublimable cyan and/or magenta and/or yellow and/or black or other dyes. Such dyes are disclosed in U.S. Pat. Nos. 4,541,830, 4,541,830, 4,698,651, 4,695,287, 4,701,439, 4,757,046, 4,743,582, 4,769,360 and 4,753,922, the disclosures of which are hereby incorporated by reference. Thus, one-, two-, three- or four-color elements (or higher numbers also) are included within the scope of the invention. 
     In a preferred embodiment of the invention, the dye-donor element comprises a poly(ethylene terephthalate) support coated with sequential repeating areas of magenta, yellow and a dye as described above which is of cyan hue, and the above process steps are sequentially performed for each color to obtain a three-color dye transfer image. Of course, when the process is only performed for a single color, then a monochrome dye transfer image is obtained. 
     Thermal printing heads which can be used to transfer dye from the dye-donor elements of the invention are available commercially. There can be employed, for example, a Fujitsu Thermal Head (FTP-040 MCSOO1), a TDK Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3. 
     A thermal dye transfer assemblage of the invention comprises 
     a) a dye-donor element as described above, and 
     b) a dye-receiving element as described above, the dye-receiving element being in a superposed relationship with the dye-donor element so that the dye layer of the donor element is in contact with the dye image-receiving layer of the receiving element. 
     The above assemblage comprising these two elements may be preassembled as an integral unit when a monochrome image is to be obtained. This may be done by temporarily adhering the two elements together at their margins. After transfer, the dye-receiving element is then peeled apart to reveal the dye transfer image. 
     When a three-color image is to be obtained, the above assemblage is formed three times using different dye-donor elements. After the first dye is transferred, the elements are peeled apart. A second dye-donor element (or another area of the donor element with a different dye area) is then brought in register with the dye-receiving element and the process repeated. The third color is obtained in the same manner. 
    
    
     The following examples are provided to illustrate the invention. 
     EXAMPLE 1 
     A known weight (approximately 1 mg) of dye as identified in Table 1 was dissolved in sufficient acetone to provide a solution of 0.01 g dye/L. A spectrum of this solution was obtained on a recording spectrophotometer and the absorption maximum was recorded as follows: 
     
                       TABLE 1                                                     
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        Absorption             Absorption                                 
        Maximum                Maximum                                    
Cmpd.   (nm)           Cmpd.   (nm)                                       
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1       584            10      580                                        
2       586            11      592                                        
3       579            12      653                                        
4       653                                                               
5       581            C-1     658                                        
6       650            C-2     663                                        
7       589            C-3     578                                        
8       595            C-4     612                                        
9       593            C-5     632                                        
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     The structure of the control dyes are as follows: ##STR7## 
     The above results indicate that the dyes of the invention in general are either of superior cyan hue (absorption maximum at higher wavelength, thus less bluish hue). While controls C-5 and C-6 have good cyan hue, they have poor light stability as will be shown hereinafter in Example 2. 
     EXAMPLE 2 
     Individual cyan dye-donor elements were prepared by coating on a 6 μm poly(ethylene terephthalate) support: 
     1) a subbing layer of Tyzor TBT®, a titanium tetra-n-butoxide, (duPont Company) (0.16 g/m 2 ) coated from 1-butanol; and 
     2) a dye layer containing each of the cyan dyes identified below and illustrated above, (0.32 mmoles/m 2 ) and FC-431® fluorocarbon surfactant (3M Company) (0.01 g/m 2 ) in a cellulose acetate propionate binder (2.5% acetyl, 45% propionyl) (at 1.5 times the weight of dye) coated from butanone. 
     On the back side of the dye-donor element was coated: 
     1) a subbing layer of Tyzor TBT®, a titanium tetra-n-butoxide, (duPont Company) (0.16 g/m 2 ) coated from 1-butanol; and 
     2) a slipping layer of Emralon 329®, a dry film lubricant of poly(tetrafluoroethylene) particles, (Acheson Colloids Co.) (0.54 g/m 2 ) coated from a n-propyl acetate, toluene, isopropyl alcohol and n-butyl alcohol solvent mixture. 
     Control dye-donors each with the cyan dye identified below (0.32 mmoles/m 2 ) were also prepared. Dye-receiving elements were prepared by coating the following layers in order on white-reflective supports of titanium dioxide pigmented polyethylene overcoated paper stock: 
     (1) A subbing layer of poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid) (14:79:7 wt. ratio) (0.08 g/m 2 ) coated from butanone solvent, and 
     (2) A dye-receiving layer of Fluorad FC-431® (a perfluorosulfonamido surfactant of 3M Corp.) (0.02 g/m 2 ), Makrolon 5700®, a bisphenol-A polycarbonate of Bayer AG, (2.9 g/m 2 ) and polycaprolactone (0.81 g/m 2 ) coated from dichloromethane solvent. 
     The dye side of the dye-donor element approximately 10 cm×15 cm in area was placed in contact with the polymeric receiving layer side of the dye-receiver element of the same area. The assemblage was fastened to the top of a motor-driven 60mm diameter rubber roller and a TDK Thermal Head L-231 (No. 6-2R161 thermostatted at 26° C., was pressed with a spring at a force of 36 Newtons against the dye-donor element side of the assemblage pushing it against the rubber roller. 
     The imaging electronics were activated and the assemblage was drawn between the printing head and roller at 6.9 mm/sec. Coincidentally, the resistive elements in the thermal print head were pulsed at 128 μsec intervals (29 μsec/pulse) during the 33 msec/dot printing time. The voltage supplied to the print head was approximately 23.5 v resulting in an instantaneous peak power of approximately 1.3 watts/dot and a maximum total energy of 9.6 mjoules/dot. A stepped density image was generated by incrementally increasing the pulses/dot through a defined range to a maximum of 255. 
     After printing, the donor element was separated from the receiving element and the Status A reflection density of the maximum density of the stepped image was read. Each stepped image was then subjected to exposure for 2 weeks, 5.4 kLux fluorescent light at approximately 25% RH. The densities were then re-read to determine the percent dye loss due to light fade. These values recorded below indicate that the dyes of the invention are superior to prior art dyes for transfer using a thermal head, and in general show dye loss equal or less to prior art dyes. 
     
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           Status A Red Density                                           
Dye In Donor Maximum Transferred                                          
                            Percent Loss                                  
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Compound 1   1.5            -4                                            
Compound 4   1.6            -3                                            
C-1 (Control)                                                             
             1.0            -5                                            
C-2 (Control)                                                             
             1.3            -4                                            
C-3 (Control)                                                             
             1.0            -3                                            
C-5 (Control)                                                             
             0.9            -38                                           
C-6 (Control)                                                             
             1.9            -30                                           
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     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.